My newly acquired MK VI was not igniting the primers in about 40% of the 45 acp moon clip rounds I was firing. The firing pin was striking the primers on the periphery at the 3 o'clock position. The firing pin looks perfectly symmetrical. When I first got it, I disassembled it completely for a thorough cleaning. I had noticed that one of the little prongs at the end of the mainspring was missing about a quarter of its length, compared to the other prong.

Took it to the gunsmith because of the misfirings. He was certain that the one short prong at the mainspring tip was absolutely to blame for the off center primer strikes. So he put in a new mainspring.

Took it to the range again. Now its "only" misfiring about 5% of the rounds. Strikes are still at the 3 o'clock position on the primer, but the new replacement mainspring is SO STIFF it is just hitting them a lot harder than the original.

Problem is the trigger pull is now outrageously heavy. Single action is WAY over 8 pounds ( my gauge only goes up to 8 pounds) and double action must be 30 pounds. My gunsmith suggested sanding down the sides of the mainspring until the pull weight becomes acceptable.

Six pounds double action, 2 1/2 pounds single action. The firing pin strike is not normal. Either the hammer is slightly bent or the cylinder is off because of pawl wear.
The full moon clips can be too thin as well. Since they hold the cases to be struck,if too far away you will get duds.
Also the firing pin tip could have been reground to prevent piercing of the primers.

Tin Can Sailor
'Nam Vet
NRA Endowment Member
President New Mexico Military Surplus Rifle Pistol Shooters

Whoa, that is light! After reading your reply I took out the replacement mainspring and ground it down considerably. These new Webley mainsprings are incredibly robust and thick compared to the old original mainsprings.

Mine is now at 3 1/2 pounds SA, and estimate 9 pounds DA (my gauge only goes up to 8 pounds, but it breaks about a centimeter beyond the 8 pound mark). When the original mainspring was in, the SA was at 8 pounds.

If you're still getting light strikes, try a box or two of Federal American Eagle ammo or if you reload use Federal primers. Federal's primers have the about the softest primer cup material and take less hammer energy to set off which generally will translate into greater ignition reliability.

CCI primers are at the other end, having much harder primer cup material, so avoid Blazer, Speer, and Lawman ammo.

Finally, you didn't specify but don't use the synthetic rubber Rim-Z moon clips if you're having ignition problems. Stick with the steel ones. The rubbery material absorbs hammer energy and effectively reduces transmitted energy to the primers.

One of my old Webleys has a weak mainspring that provides a great feeling DA trigger but I only get 100% ignition with Federal primers. Since I reload all my Webley ammo this is not a problem for me.

Turns out my ground down mainspring was hardly making a dent in the primer, though it sure felt sweet and smooth with a 3 1/2 SA pull. Couldn't ignite a single cartridge. So I threw it out and put in another new stiff mainspring only slightly lightened. SA is now about 9 pounds but ignition is certainly better.

For what it's worth, my Webley with the weak mainspring will set off Winchester primers about 90% of the time but (so far) I'm getting 100% ignition with Federal primers.

Winchester primers are softer than CCI's, but not as soft as Federal. Since you reload, trying 100 Federal primers will be a minimal expense and a good experiment. I will be interested in seeing if your results match mine. Please post your results.

For what it's worth, my Webley with the weak mainspring will set off Winchester primers about 90% of the time but (so far) I'm getting 100% ignition with Federal primers.

Winchester primers are softer than CCI's, but not as soft as Federal. Since you reload, trying 100 Federal primers will be a minimal expense and a good experiment. I will be interested in seeing if your results match mine. Please post your results.

-Bob

Good info, Bob, I leaned this years back(in the bullseye game) and as usual had forgotten this. Will try Federals and put the original spring back in.
Steve